Objective To explore the value of serum CA125 in prediction of the first-trimester threatened abortion.Methods The serum CA125 level of 78 patients with threatened abortionand( miscarriage success group and failure group) and 40 normal early pregnant women before treatment and after 1 ～ 4 weeks were tested by chemiluminescent immunoassay(CLIA) methods and the results were compared.Results The serum CA125 level of the failure group was significantly higher than that of the miscarriage success group[ (28.52 ± 19.12) x 103 U/L] and normal early pregnant women group [ (20.45 ± 9.55) × 103 U/L] ( t =- 1.28,- 1.24,all P ＜ 0.05 ),and it increased by degree and by time,and the sensitivity and specificity of detection was 93.1％ and 87.85％ respectively.Conclusion Monitoring of serum CA125 had highly clinical value in predicting the prognosis of threatened abortion.